Modular all-optical cross-connect

ABSTRACT

An all-optical, optical cross-connect includes first and second pluralities of multiport optical devices. Each of the first plurality of multiport optical devices have at least one input port for receiving a WDM optical signal and a plurality of output ports for selectively receiving one of more wavelength components of the optical signal. Each of the second plurality of multiport optical devices have a plurality of input ports for selectively receiving one of more wavelength components of the optical signal and at least one output port for selectively receiving one of more wavelength components of the optical signal. At least one of the first or second plurality of multiport optical devices are all-optical switches that can route every wavelength component independently of every other wavelength component. The plurality of input ports of the second plurality of multiport optical devices are optically coupled to respective ones of the plurality of output ports of the first plurality of multiport optical devices.

STATEMENT OF RELATED APPLICATION

[0001] This application claims the benefit of priority to U.S.Provisional Patent Application No. 60/276,310, filed Mar. 16, 2001,entitled “Reconfigurable Optical System.”

FIELD OF THE INVENTION

[0002] The invention relates generally to wavelength divisionmultiplexed optical communication systems, and more particularly, to amodular, all-optical cross-connect that may be employed in wavelengthdivision multiplexed optical communication systems.

BACKGROUND OF THE INVENTION

[0003] Wavelength division multiplexing (WDM) has been explored as anapproach for increasing the capacity of fiber optic networks to supportthe rapid growth in data and voice traffic applications. A WDM systememploys plural optical signal channels, each channel being assigned aparticular channel wavelength. In a WDM system, signal channels aregenerated, multiplexed, and transmitted over a single waveguide, anddemultiplexed to individually route each channel wavelength to adesignated receiver. Through the use of optical amplifiers, such asdoped fiber amplifiers, plural optical channels are directly amplifiedsimultaneously, facilitating the use of WDM systems in long-distanceoptical systems.

[0004] Recently, switching elements that provide a degree ofreconfigurability have become available. These reconfigurable opticalelements can dynamically change the path along which a given wavelengthis routed to effectively reconstruct the topology of the network asnecessary to accommodate a change in demand or to restore servicesaround a network failure. Examples of reconfigurable optical elementsinclude optical Add/Drop Multiplexers (OADM) and Optical Cross-Connects(OXC). OADMs are used to separate or drop one or more wavelengthcomponents from a WDM signal, which is then directed onto a differentpath. In some cases the dropped wavelengths are directed onto a commonfiber path and in other cases each dropped wavelength is directed ontoits own fiber path. OXCs are more flexible devices than OADMs, which canredistribute in virtually any arrangement the components of multiple WDMinput signals onto any number of output paths. FIG. 1 shows aconventional cross-connect 100 that has two input ports 101 ₁ and 101 ₂and output ports 103 ₁ and 103 ₂, which can each communicate a WDMsignal having N channels or wavelengths λ₁-λ_(N). Each WDM input andoutput port is coupled to a demultiplexer and multiplexer, respectively.Specifically, cross-connect 100 includes demultiplexers 105 ₁ and 105 ₂,and multiplexers 107 ₁ and 107 ₂. Cross-connect 100 also includes M×Mswitching fabric 109, where M is equal to N times the number of WDMinput/output ports (m). In the example shown in FIG. 1, M is equal to2N. Switching fabric 109 is traditionally an electronic switching coresuch as a digital cross-connect, however for current high capacityoptical systems this is being replaced with an optical switching system.

[0005] Unfortunately, because current OXC's optical switches have arelatively high insertion loss, they require optical-to-electricalinterfaces and regenerators into and out of the cross-connect. Whilethese regenerators overcome the problem of insertion loss andeffectively allow wavelength conversion of the signal as it traversesthe switching fabric, they substantially add to the cost of an alreadyexpensive switching fabric because a regenerator is required for eachand every wavelength that is used in the network.

[0006] Another limitation of the aforementioned conventional OXC is thatit is difficult to increase the number of input and output ports whensuch additional capacity is needed sometime after the OXC is initiallyinstalled and operational. In order to provide such modularity, theswitching fabric 109 as initially installed must include its maximumanticipated capacity, because otherwise the loss and number ofconnections increase too rapidly. In other words, it is impractical toprovide an M×M switching fabric that is itself modular. This limitationmay be mitigated to a small degree by packaging demultiplexers andmonitoring detectors outside the M×M switching fabric in modules thatcan be installed incrementally, but since the switching fabric is themost expensive component in the OXC, the advantages of providing aconventional OXC that is modular are limited.

[0007] Accordingly, it would be desirable to provide a low-loss opticalcross-connect in which modular functionality can be provided in arelatively easy and inexpensive manner.

SUMMARY OF THE INVENTION

[0008] In accordance with the present invention, an all-optical, opticalcross-connect is provided, which includes first and second pluralitiesof multiport optical devices. Each of the first plurality of multiportoptical devices have at least one input port for receiving a WDM opticalsignal and a plurality of output ports for selectively receiving one ofmore wavelength components of the optical signal. Each of the secondplurality of multiport optical devices have a plurality of input portsfor selectively receiving one of more wavelength components of theoptical signal and at least one output port for selectively receivingone of more wavelength components of the optical signal. At least one ofthe first or second plurality of multiport optical devices areall-optical switches that can route every wavelength componentindependently of every other wavelength component. The plurality ofinput ports of the second plurality of multiport optical devices areoptically coupled to respective ones of the plurality of output ports ofthe first plurality of multiport optical devices.

[0009] In accordance with one aspect of the invention, both pluralitiesof multiport optical devices are all-optical switches that can routeevery wavelength component independently of every other wavelengthcomponent. Alternatively one of the plurality of multiport opticaldevices may be optical couplers.

[0010] In accordance with another aspect of the invention, theall-optical switch includes a plurality of wavelength selective elementsthat each select a channel wavelength from among the plurality ofwavelength components received at the input port. A plurality of opticalelements are respectively associated with the plurality of wavelengthselective elements. Each of the optical elements direct one of theselected wavelength components selected by the associated wavelengthselective element to any one of the output ports independently of allother channel wavelengths.

[0011] In accordance with yet another aspect of the invention, anall-optical, optical cross-connect is provided which includes a firstset of m reconfigurable all-optical switches, where m is ∞ 3. Each ofthe reconfigurable switches have at least (m+1) prearranged ports forreceiving one or more wavelength components of a WDM optical signal. Thereconfigurable switches selectively directing any wavelength componentfrom one of the prearranged ports to any of the remaining ones of theprearranged ports independently of every other wavelength component. Asecond set of m reconfigurable all-optical switches are also provided,which each have at least (m+1) particular ports for receiving one ormore wavelength components of a WDM optical signal. The reconfigurableswitches in the second set route any wavelength component from one ofthe particular ports to any of the remaining ones of the particularports independently of every other wavelength component. Each of theprearranged ports of each reconfigurable switch in the first set ofswitches is optically coupled to a particular port of a differentreconfigurable switch in the second set of switches.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 shows a conventional optical cross-connect.

[0013]FIG. 2 shows an exemplary reconfigurable all-optical switch thatmay be employed in the present invention.

[0014]FIG. 3 shows an all-optical, optical cross-connect constructed inaccordance with the present invention.

[0015]FIG. 4 shows the regimes in which the optical cross-connects ofFIGS. 1 and 3 each require a fewer number of internal opticalconnections for various numbers of channels.

[0016]FIG. 5 compares the number of internal optical connectionsrequired for a various number of channels for both the conventionaloptical cross-connect of FIG. 1 and the inventive all-optical OXC ofFIG. 3 when each cross-connect incorporates 2, 4 and 8 WDM input ports.

[0017]FIG. 6 shows the inventive optical-cross connect in whichexpansion ports are available for increasing the capacity of thecross-connect in a modular fashion by adding additional reconfigurableoptical switches.

DETAILED DESCRIPTION

[0018] In accordance with the present invention, an all-optical, modularOXC is provided which employs reconfigurable switching elements, whichare all-optical switching elements that perform bothmultiplexing/demultiplexing functions and wavelength-selective routingfunctions. As a result, the present invention avoids the need fordistinct multiplexing/demultiplexing elements and switching elements, asrequired by the aforementioned conventional OXC's. Because the presentinvention employs such reconfigurable switching elements, the capacityof the OXC can be increased in a modular fashion. Moreover, theall-optical reconfigurable switches can be arranged to provide OXC'sthat have much lower insertion losses and are less expensive than theaforementioned conventional OXC's.

[0019] Various examples of all-optical reconfigurable optical switchesthat may be employed in the present invention are disclosed in U.S.patent application Ser. No. [PH-01-00-01], which is hereby incorporatedby reference in its entirety, and in particular FIGS. 2-4 of thatreference. The reconfigurable switching elements disclosed therein canselectively direct any wavelength component from any input port to anyoutput port, independent of the routing of the other wavelengths,without the need for any electrical-to-optical conversion. Anotherall-optical reconfigurable optical switch that provides additionalfunctionality is disclosed in U.S. patent application Ser. No.[PH-01-00-02], which is hereby incorporated by reference in itsentirety. This reference discloses an optical switching element in whicheach and every wavelength component can be directed from any given portto any other port without constraint. More specifically, unlike mostoptical switches, this switch is not limited to providing connectionsbetween a subset of input ports and a subset of output ports, or viceversa. Rather, this switch can also provide a connection between twoports within the same subset (either input or output). While the presentinvention may employ any of the aforementioned reconfigurable opticalswitches, the optical switch disclosed in U.S. patent application Ser.No. [PH01-00-02] will serve as an exemplary reconfigurable opticalswitch, and accordingly, additional details concerning this switch willbe presented below in connection with FIG. 2. Of course, those ofordinary skill in the art will recognize that the invention is equallyapplicable to an all-optical modular OXC that employs any reconfigurableoptical switch in which any wavelength component received on any inputport can be selectively directed to any output port, independent of therouting of the other wavelengths.

[0020] In FIG. 2, the reconfigurable optical switch 300 comprises anoptically transparent substrate 308, a plurality of dielectric thin filmfilters 301, 302, 303, and 304, a plurality of collimating lens pairs321 ₁ and 321 ₂, 322 _(l), and 322 ₂, 323 ₁ and 323 ₂, 324 ₁ and 324 ₂,a plurality of tiltable mirrors 315, 316, 317, and 318 and a pluralityof output ports 340 ₁, 340 ₂, . . . 340 _(n). A first filter array iscomposed of thin film filters 301 and 303 and a second filter array iscomposed of thin film filters 302 and 304. Individual ones of thecollimating lens pairs 321-324 and tiltable mirrors 315-318 areassociated with each of the thin film filters. Each thin film filter,along with its associated collimating lens pair and tiltable mirroreffectively forms a narrow band, free space switch, i.e. a switch thatroutes individual channels or wavelength components along differentpaths. The tiltable mirrors are micro mirrors such as the MEMS(microelectromechanical systems) mirrors. Alternatively, othermechanisms may be employed to control the position of the mirrors, suchas piezoelectric actuators, for example.

[0021] In operation, a WDM optical signal composed of differentwavelengths λ₁, λ₂, λ₃ and λ₄ is directed from the optical input port312 to a collimator lens 314. The WDM signal traverses substrate 308 andis received by thin film filter 301. According to the characteristics ofthe thin film filter 301, the optical component with wavelength λ₁ istransmitted through the thin film filter 301, while the other wavelengthcomponents are reflected and directed to thin film filter 302 viasubstrate 308. The wavelength component λ₁, which is transmitted throughthe thin film filter 301, is converged by the collimating lens 321 ₁onto the tiltable mirror 315. Tiltable mirror 315 is positioned so thatwavelength component λ₁ is reflected from the mirror to a selected oneof the output ports 340 ₁-340 _(n) via thin film filters 302-304, whichall reflect wavelength component λ₁. The particular output port that isselected to receive the wavelength component will determine theparticular orientation of the mirror 315.

[0022] As mentioned, the remaining wavelength components λ₂, λ₃, and λ₄are reflected by thin film filter 301 through lens 321 ₂ back intosubstrate 308 and directed to thin film filter 302. Wavelength componentλ₂ is transmitted through thin film filter 302 and lens 322 ₁ anddirected to a selected output port by tiltable mirror 316 via thin filmfilters 303-304, which all reflect wavelength component λ₂. Similarly,all other wavelength components are separated in sequence by the thinfilm filters 303-304 and subsequently directed by tiltable mirrors317-318 to selected output ports. By appropriate actuation of thetiltable mirrors, each wavelength component can be directed to an outputport that is selected independently of all other wavelength components.

[0023] Referring now to FIG. 3, shown is one embodiment of a modular,all-optical, m×m cross-connect 400 in accordance with the presentinvention. OXC 400 can route any wavelength received on any of its minput ports 412 to any of its m output ports 422 independently of oneanother. In FIG. 3, for purposes of illustration only, m is depicted asequal to 8. It should be noted that the term “route” as used hereinrefers not only to the ability to selectively direct selected one ormore wavelengths along a given path, but also the ability to prevent thetransmission of any other wavelengths not being directed along that samepath.

[0024] Cross-connect 400 includes a first series of reconfigurableoptical switches 410 ₁, 410 ₂, . . . 410 _(m) and a second series ofreconfigurable optical switches 420 ₁, 420 ₂, . . . 420 _(m).Reconfigurable optical switches 410 and 420 may be of the typeillustrated in FIG. 2. Each of the first series of reconfigurableoptical switches 410 has an input port 412 and m output ports 414. Forexample, in FIG. 3, switch 410 ₁ has an input port 412 ₁ and outputports 414 ₁₁, 414 ₁₂, . . . 414 _(1m) that are clearly visible. Theremaining switches in the first series are likewise configured.Similarly, each of the second series of optical switches 420 has anoutput port 422 and m input ports 424. For example, in FIG. 3, switch420 _(m) has an output port 422 _(m) and input ports 424 _(m1), 424_(m2), . . . 424 _(mm) that are clearly visible. The reconfigurableoptical switches in the first and second series of switches areinterconnected in the following manner. The output ports of each switchin the first series are sequentially coupled to the input ports of theswitches in the second series. For example, as can be seen in FIG. 3,output ports 414 ₁₁-414 _(1m) of switch 410 ₁ are respectively coupledto input ports 424 _(m1)-424 ₁₁ of switches 420 _(m)-420 ₁. In this waythe m² outputs of the first series of switches are coupled to the m²inputs of the second series of switches, thus forming m² internaloptical connections. It should be noted that depending on the cost ofswitches employed above relative to optical amplification, either theinput or the output series of switches can be replaced with a 1×mpassive coupler. If the input switches are replaced with a passivecoupler, this routes a copy of all the wavelengths of all the inputfibers to the second series of switches where only the desired signal ischosen to pass on. Alternately, the appropriate signals could beselected in the first series of switches, where the wavelengths areswitched on a wavelength by wavelength basis to a specific passivecoupler for a given output fiber. That coupler passively combines thewavelengths from each of the switches onto a single output fiber. Whilethe passive coupler will be less expensive than an optical switch, itadds significant loss, which in turn will require an expensiveamplifier. Hence the optimum configuration will depend on the cost ofthe switches, optical amplifiers, and the number of WDM fibers that areto be cross-connected (i.e., m).

[0025] One important advantage of the all-optical OXC shown in FIG. 3over the OXC shown in FIG. 1 is that when a large number of WDM channelsare employed, the number of internal optical connections is far fewer inthe OXC of FIG. 3 than in the OXC of FIG. 1. This is becoming anincreasingly important factor as the number of WDM channels used inoptical transmission systems has increased in recent years from 16 to32, to even upwards of 160 channels in the most recent systems. In theOXC shown in FIG. 1, for instance, the number of internal connections is2 mN, where m is the number of input and output ports on which WDMsignals are communicated to and from the OXC, and N is the maximumnumber of channels in the WDM signal. In comparison, the inventive OXCshown in FIG. 3 has m² internal optical connections. In other words, inthe present invention, the number of interconnections scales with thenumber of WDM input and output ports rather than with the number ofchannels.

[0026] For a given optical cross-connect with N channels and m WDM inputand output ports, FIG. 4 shows the regimes in which the OXCs of FIGS. 1and 3 each require fewer numbers of optical connections. In particular,when the number of WDM input and output ports is less than twice thetotal number of channels, the OXC of the present invention will requirea fewer number of optical connections, thereby reducing the cost and thephysical space occupied by the OXC. The reduction in physical space isoften particularly important for communications equipment, whichfrequently must reside in a specialized facility that is expensive toprocure on a square-footage basis. FIG. 5 shows how large thediscrepancy can be in the number of connections between the two OXC'swhen employed in current networks, where the number of channels isincreasing more rapidly than the number of WDM input and output ports.In FIG. 5 the number of internal connections required for a variousnumber of channels is shown for both a conventional OXC and theinventive all-optical OXC for 2, 4 and 8 WDM input ports. For example, aconventional 32 channel OXC having 4 WDM inputs and outputs requiresfour multipexers and four demultiplexers each designed to respectivelymultiplex and demultiplex 32 channels and a 128×128 digital switchingfabric, yielding a total of 256 internal optical connections. Incontrast, the inventive all-optical OXC can achieve the samefunctionality with 8 reconfigurable optical switches, yielding a totalof 16 internal connections. Moreover, the inventive OXC is smaller,easier to fabricate, and likely to provide lower loss.

[0027] Another important advantage of the all-optical OXC shown in FIG.3 over the OXC shown in FIG. 1 is that it can be installed and upgradedin a modular fashion. In particular, if the OXC is initially provisionedwith “x” WDM input and output ports and, hence employs a total of “2×”reconfigurable optical switches, the number of WDM input and outputports can be expanded to m (where x<m) by the addition of (m−x)additional reconfigurable optical switches. This presumes, of course,that the original x optical switches are initially provisioned with moutput ports (in the case of first series of optical switches connectedto the WDM input ports) and m input ports (in the case of the secondseries of optical switches connected to the WDM output ports). Theseadditional (m−x) ports serve as expansion ports that can be connected tothe additional (m−x) reconfigurable optical switches when suchadditional capacity is required. For example, FIG. 6 shows an OXCconstructed in accordance with the present invention that is initiallyprovisioned for 4 WDM input and output ports. As shown, thereconfigurable optical switches 610 and 620 have expansion ports 630that can be utilized when additional reconfigurable switches are to beincorporated into the OXC.

[0028] The modular functionality offered by the present invention arisesbecause only one internal optical connection is required to establish acommunication path for each and every channel between any given WDMinput port and any given WDM output port. For instance, a reconfigurableoptical switch with a total of 9 ports can reserve one port as a WDMinput or output port to the OXC while the remaining ports can be used toestablish the internal optical connections to other optical switches inthe OXC. As a consequence of this ability the present invention providesa modular OXC that can be expanded simply by adding additionalreconfigurable optical switches when extra capacity is required. In thisway the majority of the capital costs associated with the extra capacityare not incurred until the extra capacity is actually needed. Incontrast, the OXC shown in FIG. 1 requires that a substantial portion ofthe entire cost associated with increasing capacity be incurred when theOXC is initially installed.

1. An all-optical, optical cross-connect, comprising: first and secondpluralities of multiport optical devices, said first plurality ofmultiport optical devices having at least one input port for receiving aWDM optical signal and a plurality of output ports for selectivelyreceiving one of more wavelength components of the optical signal, saidsecond plurality of multiport optical devices having a plurality ofinput ports for selectively receiving one of more wavelength componentsof the optical signal and at least one output port for selectivelyreceiving one of more wavelength components of the optical signal, atleast one of said first or second plurality of multiport optical devicesbeing all-optical switches that can route every wavelength componentindependently of every other wavelength component; and wherein theplurality of input ports of the second plurality of multiport opticaldevices are optically coupled to respective ones of the plurality ofoutput ports of the first plurality of multiport optical devices.
 2. Theoptical cross-connect of claim 1 wherein the other of the first orsecond plurality of multiport optical devices are all-optical switchesthat can route every wavelength component independently of every otherwavelength component.
 3. The optical cross-connect of claim 1 whereinthe other of the first or second plurality of multiport optical devicesare couplers.
 4. The optical cross-connect of claim 1 wherein saidall-optical switch comprising: a plurality of wavelength selectiveelements that each select a channel wavelength from among the pluralityof wavelength components received at the at least one input port; and aplurality of optical elements respectively associated with saidplurality of wavelength selective elements, each of said opticalelements directing one of the selected wavelength components selected bythe associated wavelength selective element to any one of the outputports independently of all other channel wavelengths.
 5. The opticalcross-connect of claim 2 wherein each of said all-optical switchescomprising: a plurality of wavelength selective elements that eachselect a channel wavelength from among the plurality of wavelengthcomponents received at the at least one input port; and a plurality ofoptical elements respectively associated with said plurality ofwavelength selective elements, each of said optical elements directingone of the selected wavelength component selected by the associatedwavelength selective element to any one of the output portsindependently of all other wavelength components.
 6. The opticalcross-connect of claim 4 wherein said optical elements each include atiltable mirror.
 7. The optical cross-connect of claim 4 furthercomprising a free space region disposed between the input ports and thewavelength selective elements.
 8. The optical cross-connect of claim 4wherein said optical elements retroreflect said channel wavelengths. 9.The optical cross-connect of claim 4 wherein said wavelength selectiveelements are thin film filters each transmitting therethrough adifferent one of the wavelength components and reflecting the remainingchannel wavelengths.
 10. The optical cross-connect of claim 4 whereinsaid optical elements are reflective mirrors that are selectivelytiltable in a plurality of positions such that in each of the positionsthe mirrors reflect the wavelength component incident thereon to anyselected one of the output ports.
 11. The optical cross-connect of claim10 wherein said reflective mirrors are part of a micro-electromechanical(MEM) reflective mirror assembly.
 12. The optical cross-connect of claim11 wherein said reflective mirror assembly is a retroreflective mirrorassembly.
 13. The optical cross-connect of claim 10 wherein saidreflective mirrors are part of a retroreflective optical assembly. 14.The optical cross-connect of claim 10 wherein said reflective mirrorseach include a piezoelectric actuator.
 15. The optical cross-connect ofclaim 7 wherein said free space region comprises an opticallytransparent substrate having first and second parallel surfaces, saidwavelength selective element includes a plurality of wavelengthselective elements arranged in first and second arrays extending alongthe first and second parallel surfaces, respectively.
 16. The opticalcross-connect of claim 15 wherein the optically transparent substrateincludes air as a medium in which the optical signal propagates.
 17. Theoptical cross-connect of claim 15 where the optically transparentsubstrate is silica glass.
 18. The optical cross-connect of claim 15wherein said first and second arrays are laterally offset with respectto one another.
 19. The optical cross-connect of claim 18 wherein eachof said wavelength selective elements arranged in the first array directthe selected wavelength component to another of said wavelengthselective elements arranged in the second array.
 20. The opticalcross-connect of claim 4 further comprising a collimating lens disposedbetween each one of said wavelength selective elements and the opticalelement associated therewith, each of said optical elements beingpositioned at a focal point of the lens associated therewith.
 21. Anall-optical, optical cross-connect, comprising: a first set of mreconfigurable all-optical switches, where m is ∞ 3, each of saidreconfigurable switches having at least (m+1) prearranged ports forreceiving one or more wavelength components of a WDM optical signal,said reconfigurable switches selectively directing any wavelengthcomponent from one of the prearranged ports to any of the remaining onesof the prearranged ports independently of every other wavelengthcomponent; a second set of m reconfigurable all-optical switches eachhaving at least (m+1) particular ports for receiving one or morewavelength components of a WDM optical signal, said reconfigurableswitches routing any wavelength component from one of the particularports to any of the remaining ones of the particular ports independentlyof every other wavelength component; and wherein each of the prearrangedports of each reconfigurable switch in the first set of switches isoptically coupled to a particular port of a different reconfigurableswitch in the second set of switches.
 22. The optical cross-connect ofclaim 21 wherein each of said m reconfigurable switches in the first setof switches have at least (m+2) prearranged ports and said mreconfigurable switches in the second set of switches have at least(m+2) particular ports.
 23. The optical cross-connect of claim 21wherein each of said all-optical switches comprising: a plurality ofwavelength selective elements that each select a wavelength componentfrom among the wavelength components of the WDM optical signal receivedat one of the input port; and a plurality of optical elementsrespectively associated with said plurality of wavelength selectiveelements, each of said optical elements directing one of the selectedwavelength components selected by the associated wavelength selectiveelement to any one of the ports independently of all other channelwavelengths.
 24. The optical cross-connect of claim 23 wherein saidoptical elements each include a tiltable mirror.
 25. The opticalcross-connect of claim 23 further comprising a free space regiondisposed between the ports and the wavelength selective elements. 26.The optical cross-connect of claim 23 wherein said optical elementsretroreflect said channel wavelengths.
 27. The optical cross-connect ofclaim 4 wherein said wavelength selective elements are thin film filterseach transmitting therethrough a different one of the wavelengthcomponents and reflecting the remaining wavelength components.
 28. Theoptical cross-connect of claim 23 wherein said optical elements arereflective mirrors that are selectively tiltable in a plurality ofpositions such that in each of the positions the mirrors reflect thewavelength component incident thereon to any selected one of the outputports.
 29. The optical switch of claim 28 wherein said reflectivemirrors are part of a micro-electromechanical (MEM) reflective mirrorassembly.
 30. The optical cross-connect of claim 29 wherein saidreflective mirror assembly is a retroreflective mirror assembly.
 31. Theoptical switch of claim 28 wherein said reflective mirrors are part of aretroreflective optical assembly.
 32. The optical switch of claim 28wherein said reflective mirrors each include a piezoelectric actuator.33. The optical switch of claim 25 wherein said free space regioncomprises an optically transparent substrate having first and secondparallel surfaces, said wavelength selective element includes aplurality of wavelength selective elements arranged in first and secondarrays extending along the first and second parallel surfaces,respectively.
 34. The optical switch of claim 33 wherein the opticallytransparent substrate includes air as a medium in which the opticalsignal propagates.
 35. The optical switch of claim 33 where theoptically transparent substrate is silica glass.
 36. The optical switchof claim 33 wherein said first and second arrays are laterally offsetwith respect to one another.
 37. The optical switch of claim 36 whereineach of said wavelength selective elements arranged in the first arraydirect the selected wavelength component to another of said wavelengthselective elements arranged in the second array.
 38. The optical switchof claim 23 further comprising a collimating lens disposed between eachone of said wavelength selective elements and the optical elementassociated therewith, each of said optical elements being positioned ata focal point of the lens associated therewith.